Field of the Invention
The invention relates to an optical device having improved impact resistance, and more particularly to an optical device having improved impact resistance, which is used in an image pickup apparatus, such as a film camera or a digital camera.
Description of the Related Art
There has been known a photographic lens barrel provided with a zoom mechanism for moving a plurality of optical lenses along the optical axis to thereby change the photographing magnification. The zoom mechanism includes, for example, a type in which a lens holding frame holding an optical lens is engaged with cam grooves of a rotary cam barrel, and the lens holding frame is moved along the optical axis while restricting rotation of the lens holding frame using a rectilinear motion barrel.
In the photographic lens barrel thus constructed, it is required to improve impact resistance so as to prevent disengagement of the components when an external force, such as an impact, acts on the photographic lens barrel. To improve the impact resistance of the photographic lens barrel, there have been proposed a method of strengthening the whole photographic lens barrel by increasing the rigidity of each component, and a method of using elastic members for some of the components of the photographic lens barrel and further absorbing an impact by filling cushioning material therebetween.
As the method of increasing the rigidity of each component, there has been employed a method of selecting a stronger material, a method of increasing the thickness of each component, a method of reinforcing the peripheral portions of shock-sensitive components, etc. Further, in this method of reinforcing the peripheral portions of shock-sensitive components, the construction itself of the photographic lens barrel and the shape of each component are elaborately designed. For example, there has been proposed a construction in which a rear group lens-holding frame has an outer shape configured to support, from inside, the follower pins of a front group lens-holding frame for cam-driving the lens holding frames, so as to prevent the follower pins from being disengaged from the cam grooves of a cam ring when an impact is applied to the photographic lens barrel due to a drop or the like (see Japanese Patent Laid-Open Publication No. 2012-242727). By applying the above-mentioned relationship to a plurality of lens groups within the photographic lens barrel to provide a structure in which the lens holding frames support each other, it is possible to improve the impact resistance of the photographic lens barrel to prevent the cam followers from being disengaged due to an impact, thereby contributing to improvement of reliability of the photographic lens barrel.
However, in the invention disclosed in Japanese Patent Laid-Open Publication No. 2012-242727, the outer shape of the rear group lens-holding frame is configured to support the follower pins of the front group lens-holding frame from inside, and hence the thickness of the overlapping portions of the lens holding frames is increased in the radial direction. Therefore, with an increase in the number of lens groups arranged such that they have the above-mentioned relationship, the outer diameter of the front group lens-holding frame is increased. As a consequence, the outer diameter of the photographic lens barrel is increased, resulting in an increase in the size of the whole image pickup apparatus.